Astigmatism Summary
Astigmatism is a common eye condition that's easily corrected by eyeglasses, contact lenses, or surgery. Symptoms of astigmatism are headaches, fatigue, eyestrain and blurred vision.
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What is astigmatism?

Astigmatism is an irregularity in the way light is focused (refracted) by the eye. Most commonly, astigmatism is a result of variations in the curvature of the cornea of the eye. However, astigmatism can also be caused by similar irregularities in the curvature of the lens of the eye.

Astigmatism is classified as “regular” if the irregularity is easily corrected with glasses or contact lenses, such as when the cornea takes on the shape of a football (steeper in one axis, flatter in the opposite axis) as opposed to a sphere. It is classified as “irregular” if the curvature is more variable, or if the steepest portion is off-center.

What are the risk factors for astigmatism?

Most regular corneal astigmatism develops for unknown reasons and may be inherited. Some astigmatism can be acquired when the cornea's curvature is altered by outside forces such as the weight of a droopy eyelid, a suture, a scar, or a condition that alters the cornea's structure. This occurs, for example, in a condition called keratoconus, whereby the cornea becomes cone-shaped.

What are the symptoms and signs of astigmatism?

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The symptom of astigmatism is poorly-focused vision that causes blurring. This blurring can often be corrected with glasses or contact lenses. The principal finding in examining for astigmatism is an irregular curvature (such as football shape) to the cornea and/or lens. This may require specialized testing to detect and measure.

How is astigmatism diagnosed?

Astigmatism is diagnosed during the measurement for glasses (refraction). The eye's overall astigmatism can be measured objectively by a manual technique using a device called a retinoscope, or automatically with an autorefractor machine. Subjectively, a patient can determine the necessary astigmatism correction by choosing from several different powers of lenses. The various lens powers are presented to the patient while viewing a chart through a phoropter.

Distinguishing which portion of the astigmatism is arising from the cornea versus arising from the lens can be important, particularly when fitting a contact lens or planning a surgical procedure. This can be done by examining the shape of the cornea with studies such as topography and keratometry. Wavefront analysis is another tool that is useful in evaluating irregularities in the way the eye focuses light.

If the astigmatism is found to be irregular, further studies may be necessary. A thorough eye examination including a slit lamp examination can be used to detect external forces that are warping the cornea (such as drooping eyelid, suture, scar, and others). If the cornea's shape is irregular due to a suspected corneal disease (such as keratoconus, pellucid marginal degeneration, post-LASIK ectasia, and more) further studies may be necessary to confirm the suspected diagnosis.

Medically Reviewed by a Doctor on 6/25/2013

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